Backup storage devices are used for backing up information on servers and other network machines or devices. Backup storage devices are often used to backup various types of information including, for example, files, databases, system information and files, etc.
When one backup storage device is shared among a plurality of host devices, problems may arise when accessing the storage device to read or write to it. An example of a local area network (LAN) including backup storage is shown in FIG. 1A. The LAN includes one or more workstations 5a-5n, one or more servers 6a-6n and at least one backup storage device 7 interconnected via a network 9. Each of the workstations 5a-5n and servers 6a-6n my utilize different operating systems. Backup storage device 7 may be, for example, a tape device such as a tape library. If host devices such as the workstations 5a-5n or servers 6a-6n are sharing the same storage device 7, each operating system may attempt to store data in the same location on the storage device 7. In this case, data required by one host device might be overwritten by data from a subsequent write by another host device. In addition, some operating systems may store special information at specific addresses of the storage device. Some oilier operating ‘systems may require that any attached storage devices have identifying information stored in one or more portions of that same area of storage. This results in conflicts and difficulties in providing such shared storage. A controller may be used to control access to the storage device 7. However, should the controller crash, the storage system data may be permanently lost.
Multiple storage devices may be provided for backing up data on host devices. However, managing multiple storage devices in an efficient and effective manner allowing backup and recovery for multiple hosts can be time and resource consuming and can utilize much of the bandwidth of the LAN or wide area network (WAN).
A storage area network (SAN) may be used to free up bandwidth on the LAN or WAN. A SAN is a high speed storage network of shared storage devices. A SAN makes all storage devices available to all hosts on the LAN or WAN, saving valuable bandwidth on the LAN or WAN.
FIG. 1b depicts a SAN environment. The SAN includes a plurality of distributed servers 2a-2n, connected to one or more storage devices such as backup libraries 4a-4n, via a highspeed network 3. The backup devices 4a-4n may include, for example, tape libraries each including a plurality of storage media, a picker and one or more read/write devices for reading and writing to the storage media. The distributed servers 2a-2n and the backup devices 4a-4n may be interconnected via a high speed/high volume network 3 that may include various highspeed switches and/or bridges. With this type of environment, there are several ways that the servers 2a-2n and backup devices 4a-4n can be shared. For example, one of the servers 2a-2n may act as a chief arbitrator granting access of backup devices 4a-4n to all other servers. This is often referred to as a master/slave system. In a master/slave system, the intelligence lies with the master and the master has sole discretion and decision making authority regarding when and if to allow servers to access a backup device. The master creates and maintains information regarding the state of each of the devices on the network.
One problem with the master/slave system is that if the master crashes, it may take a lot of time and effort to configure another server as the master. All other servers will wait until another master server has been designated and configured by the system administrator. The new master will then re-inventory the network, and build up information regarding the state of each device on the network. This can be a time consuming and costly procedure.
Another approach is to partition access of a backup device among the servers, so that each server is capable of accessing only the drives and slots in the library within its partition. However, this system may not make the most efficient use of the backup devices.
In many backup operations, the backup application reads the data from the primary storage device to the server memory, does necessary formatting, and sends it to the appropriate backup storage devices. These processes involve heavy utilization of CPU, I0 channels and the system memory. It is quite possible that when backup operations are in progress, the servers may not be able to perform any other application processing. This is one of the reasons why system administrators prefer to perform backup at a time when the application load on the server is at a minimum. It would be beneficial if the backup operations could be performed without requiring heavy utilization of the server system, thereby freeing up the server even during information backup.